1. Field of the Invention
The present invention relates to a method and apparatus for converting a black and white image into a color image by means of a light color changing device driven by a color image signal which has been resolved into its color components.
2. Description of the Related Art
Apparatus which display the black and white image displayed on a black and white display as color images, achieve this by arranging, on the front of a black and white monitor screen, liquid crystal shutters which can selectively pass the three primary colors namely red, green and blue from an incident white light. A changing signal corresponding to the signal for the black and white display is input to the liquid crystal shutter, and as a result the black and white image on the black and white display appears as a color image.
In displaying a color image using such a liquid crystal element however, particularly in the case of a moving color image, the following problems arise.
That is to say, with a normal television image, instead of changing the number of scanning lines to increase the resolving power, so called interlace scanning which scans odd and even number fields with the fields shifted by half the distance between the scanning lines is carried out. In this way the vertical resolving power of the image can be maintained by shifting of the scanning positions relative to each other without increasing the field cycle.
In the case of a color display, a color image signal which has been resolved into its red, green and blue (denoted hereafter by R, G, B) color components is simultaneously scanned to effect color display. With the before-mentioned apparatus using a liquid crystal shutter however, R, G, B signals are alternately input, and a light signal for each color component is selectively output. As a result, if for example the simultaneously input R, G, B, field image signal is only simply rearranged into a one line sequence, and output as a serial signal, it is not possible to display all of the input signal, and as a result at least 2/3 of the field is discarded. Consequently, the original image reproduction ratio for the time axis direction drops to 1/3, so that a real time moving image cannot be displayed. As a simple method to overcome this problem, it is possible to output the field image signal by switching the color components for each field. However in this method, the period for the color image display of an R, G, B unit is trebled, and since there is a single field time shift in the image for each color component, an undesirable color shift occurs in the moving part of the image display.
It has been considered to output the R, G, B image signals of the simultaneously input single fields as a serial signal which has been sped up 3 times. If this is done, the color resolved R, G, B image signal can be scanned at three times the speed. As a result, the color image of a single field can be displayed with a predetermined cycle, and thus satisfy the high speed characteristics. However, in this case, since the fields are input as a succession of the odd number field and even number field three times for each R, G, B image signal, the balance of the alternating pattern for the odd number field and the even number field on the display side collapses. Some method of overcoming the above problems is thus required.